Embodiments of the inventive concepts relate to a support unit, a substrate treating apparatus including the same, and a method for treating a substrate.
Plasma is generated by very high temperature, a strong electric field, or radio-frequency (RF) electromagnetic fields. The plasma means an ionized gas state including ions, electrons, and/or radicals. When a semiconductor device is manufactured, an etching process using plasma may be performed. Ion particles contained in the plasma may collide with a substrate, and thus the etching process may be performed.
FIG. 1 shows a focus ring before and after a substrate treating process in a substrate treating apparatus. A transverse X-axis means a distance from a center of a support unit. A longitudinal Y-axis means a thickness of the focus ring. The focus ring may also be etched when a process of etching a substrate is performed using plasma, and thus the thickness of the focus ring may be reduced.
FIG. 2. shows an incident path of etching ions incident toward a pattern of a substrate. A right solid arrow shows an incident direction of the etching ions in an early stage of a process. When RF power is supplied to an electrode plate of a support unit, an electric field may be generated over the electrode plate, and an incident angle of the etching ions may be affected while the etching ions pass through the electric field. In the early stage of the process, the etching ions may be incident toward the focus ring (i.e., an edge of the substrate). When the focus ring is etched while performing the process, the electric field may be changed. Thus, the incident angle of the etching ions may be changed. As the process proceeds, the incident direction of the etching ions may move toward a center of the substrate. A dashed line arrow shows an incident direction of etching ions after the process or in a later stage of the process. In the example of FIG. 2, the incident angle of the etching ions may be changed counterclockwise. Thus, an undesired surface of the substrate may be etched to lower the accuracy of the process. A slope critical dimension (SCD) means a horizontal distance from a center of a depressed portion between patterns of the substrate to a point on which the etching ions are incident. A direction from the center of the depressed portion toward the focus ring (i.e., the edge of the substrate) has a positive value, and a direction toward a center of the substrate has a negative value.
FIG. 3 is a graph showing a variation of a slope critical dimension (SCD) according to a process time. The SCD may be gradually reduced as the process time passes. In other words, the incident direction of the etching ions may be changed in the direction toward the center of the substrate. Thus, a spot different from a desired etching spot may be etched to deteriorate the accuracy and efficiency of the etching process. Meanwhile, to prevent these problems, the focus ring may be periodically replaced with new one. However a replacement period of the focus ring may be short and a maintenance cost of the focus ring may increase.